Supporting structure for screen stretcher bars



March 3, 1953 P. c. BYE 2,639,225

SUPPORTING STRUCTURE FOR SCREEN STRETCHER BARS Filed July 11, 1949 2 SHEETS-SHEET l IN VEN TOR.

B38401. C. BYE,

flag M ATTORN YS March 3, 1953 P. C. BYE

SUPPORTING STRUCTURE FOR SCREEN STRETCHER BARS Filed July 11, 1949 iv 95c 06 2 Sl-EETS-SHEET 2 INVENTOR.

5401. C: BYE,

ATTORNEYS Patented Mar. 3, 1953 UNITED STATES PATENT OFFICE SUPPORTING STRUCTURE FOR SCREEN STRETCHER BARS 9 Claims.

The present invention relates generally to material handling or classifying screens, and more particularly to means for fastening a screen in place in a screen box or other support. The invention is illustrated as applied to a multipledeck vibrating screen machine because it has especial advantages therein; but they invention is not necessarily limited thereto.

In screening machines for sorting, separating, or classifying materials, various devices have been used for fastening the screen in place in a box or the like which supports the screen. One arrangement has been a clamp-like member, usually termed a stretcher bar, which is a relatively heavy, rigid member mounted on the box or other support in a manner to engage the screen and stretch it when a bolt or the like is tightened. When the bolt is released, in the conventional construction, the stretcher bar is not supported in place so it falls of its own weight onto the screen, binding the screen against the support.

In the usual commercial machine, the stretcher bar is heavy and it is difiicult to remove the screen without injury to it if it is of small gauge wire. But the real difficulty is encountered in replacing the screen because the screen cannot be slid into place between the support and the stretcher bar unless the bar is held up clear of the supports. insert the screen, as one must hold up the stretcher bar at each side of the screen. However, there are many times when the stretcher bars must be completely removed from the machine because the design of the machine, as in multiple-deck machines, is such that the bars cannot be reached to be manually held clear of the support. Thi may require removal of higher screens, particularly in enclosed dusthoused machines. This assembly and disassembly work is considerable, and the result in any case is that a machine is out of operation for asubst-antial length of time whenever a screen must be removedzand replaced.

Hence, it is a general object of my invention to provide a structure for supporting a stretcher bar free of the screen support when the bar is moved to a position in which the bar releases the screen allowing it to be removed or replaced, and yet the structure permit the stretcher bar to move to. a position-in which it firmly engages the screen to, hold, it tight.

It is also .an object of my invention to provide .a structure for supporting'a stretcher bar firmly in engagement with the screen Within a range of At best it requires two men to 2 positions to accommodate screens of different widths and thicknesses, to adjust tension invthe screen, or otherwise vary conditions.

A further object is to provide means for supporting a stretcher bar in such a position that the associated screen may be freely removed or inserted in the-box. or other screen support without removing the stretcher bar and without disturbing other screens above or below.

It is also an objectto provide a supporting structure of the character described that supports the stretcher bar over a range of positions without becoming loose or slack.

The above and otherobjects-of'myinvention have been attained in a screen tensioningand supporting structure having a screen support and a stretcher bar supported thereon for engaging the screen, by providing aresilient member for supporting the stretcher bar clear of the screen when screen tension is relaxed. Some type of screen tensioning means, suchas a nut and bolt, interconnects the screen support and the stretcher barto draw the latter toward the screen support for applying tension to the screen.

The resilient nature of the stretcher bar support does not interfere with this movement; yet when the tensioning means is released, the bar is fully supported against gravity and does not fall down onto the-screen. As aresult'the screen is free to move relative to thescreen support without any hindrance during removal or replacement of the screen.

The support for the stretcher bar is preferably a spring interposed between the screen support and the stretcher bar. Either a coil or a torsion spring may be used with good results. The torsion spring can advantageously be mounted on the screen support in a manner to permit up-and-d-own adjustment of the spring and the stretcher bar.

How the above objects and advantages of my invention, as well as others not specifically-referred to herein, are attained will be more readily understood by reference to the following description and the annexed drawings, inwhich:

Fig. 1 is a side elevation of adouble-deckvitbrating screen machine embodying myinvenion;

Fig. 2 is a fragmentary vertical section on line 2-2 of Fig. 1 showing separate stretcher bars engaging the upper and lower screens;

Fig; 3 is a fragmentarysection on line 3-3 of Fig. 2;

Fig. 4 is a fragmentary-sectionsimilar to; Fig. 2 but showing only the top stretcher'ban which ing over a pulley attached to shaft ll.

is in released position and held clear of the screen;

Fig. 5 is a fragmentary vertical elevation as on line 5-5 of Fig. 4, with the screen omitted;

Fig. 6 is a fragmentary vertical section and elevation taken generally on line 66 of Fig. 4 but omitting the stretcher bar and showing the stretcher bar supporting pring in elevation; and

Fig. 7 is a fragmentary section comparable to Fig. 2, showing a modified form of my invention as applied to a single screen.

Referring now to the drawings, there is shown in Fig. 1 a side view of a typical multiple-deck vibrating screen machine. The device comprises a screen support or box, indicated generally at [0, mounted upon a fixed foundation l2 by means of some suitable type of resilient mounting means, as for example spiral springs l4. Springs I4 permit the screen support box ID to vibrate with respect to the foundation. Box l comprises generally a pair of parallel spaced side members l which are interconnected by a plurality of transverse members [6, which may be structural members of any suitable shape. The screen support box I!) is normally open at its ends in order to facilitate entry and discharge of materials passing over the screen. This passage of material is assisted by the action of gravity, and for that reason the box is inclined, as shown in Fig. l, at such an angle as to produce a desirable rate of travel of the material over the screens. Vibration of box In and the screens attached thereto is obtained by rotating shaft I! by suitable drive means, not shown, such as a belt pass- Shaft I"! carries an eccentric weight l9, which is conventionally formed in the shape of a half circle, mounted in a fly-wheel i 8 secured to the shaft. As shaft l! i rotated, unbalanced forces are produced by the rotating weight l9 and these forces induce strong vibrations of support box I0 and the screens carried thereby.

A portion of one side of the screen support and the screens carried thereby is shown in transverse cross-section in Fig. 2, the device being a double-deck machine with one screen mounted above the other. The upper screen 22 is of relatively large mesh and is woven from wire of relatively large size. ihe lower screen 23 is also of the woven wire cloth type, but is of relatively smaller mesh and i woven from wire of correspondingly smaller diameter.

As mentioned above, screen support box I0 consists of two parallel side members [5 located at opposite sides of the screens, one of these side members being shown in Fig. 2. It may be a structural member of any suitable shape, and is shown as a channel member providing a vertical side wall [5a. The other side member is exactly the same as the one shown in Fig. 2 except that its parts are reversed as it is on the opposite side of the machine. Both screens 22 and 23 are supported at their lateral edges by side members 15 as will be further described and are held tightly extending intermediate screen supports are ried by transverse members I6.

In order to hold a screen in place, it is engaged along each of two opposite sides by a stretcher bar 33, as shown particularly in Fig. 2. These stretcher bars preferably extend substantially the full length or" the screens, as indicated in Fig. 1. Each stretcher bar is of angular outline when viewed in cross-section and is preferably generally channel shaped, except that the web or back 30a of the channel is preferably not at right angles to the two legs of the channel.

The edge of the upper leg 30b of the stretcher bar bears against the inside face of the side wall l5a of the support member [5 and the stretcher bar pivots or rocks about the position of this engagement with respect to the member I5. The lower leg 30c of the stretcher bar engages the edge of the screen. When the screen is made of relatively heavy wire, as is screen 22, it is ordinarily sufficient to bend back the transverse wires of the screen to form hooks at their ends which may be engaged by the stretcher bar, as shown in the upper portion of Fig. 2. When the screen is made of a lighter wire, it is preferable to provide a metal reinforcing strip or binder along the edge of the screen, as indicated at 3| along the edge of screen 23 in Fig. 2. The metal reinforcing strip is sufficiently rigid that it does not straighten out under the forces applied to tension the screen. Rather than to draw the screen tightly against the inside vertical face of the support member, each side support member I5 is preferably provided with an inwardly projecting ledge of some type, as afforded by the upper surface of angle member l5b which is suitably attached to, and forms a part of, the support member. The stretcher bar thus can force the screen downwardly against the upper surface of this an le member in order to hold the screen tightly in place and also form a seal or barrier along the edge of the screen which prevents the material from passing over the edge of the screen.

The stretcher bar 39 and the screen support l5 are interconnected by suitable means for pulling the stretcher bar towards the support member and thus applying tension to the screen. This screen tensioning means may conveniently be bolt 33 Which passes through the stretcher bar and also through the side wall 15a of member l5. Each stretcher bar is preferably provided with a plurality of these tensioning means, such as bolts 33, spaced at intervals along the length thereof and extending through the adjacent support member l5, as indicated in Fig. 1. Bolt 33 has a square shank portion 33a adjacent the head 33b, as in a carriage bolt, and is held against rotation by plate 34 which has a square opening in it to receive the square portion of the bolt, as indicated in Fig. 3. The head 331) at the inner end of the bolt bears against the inner face of the stretcher bar or the plate 34, so as to exert an outward thrust against the stretcher bar. The other end of the bolt is threaded and extends outwardly beyond support member l5 where nut 35 is screwed on to the end of the bolt. Nut 35 has a spherically shaped surface at its inner end which rests against a similarly spherically shaped seat 35 provided on the support member 15. Of course, the spherical seat may be provided upon a separate member, as for example a washer of a plane-concave type interposed between nut 35 and member I 5. My invention is not necessarily limited to this particular construction, but the construction is preferred because it affords means whereby the nut bears evenly against the support member even though bolt 33 shifts angularly with respect to the support member.

Interposed between the stretcher bar and the screen support member If: is a resilient member for supporting the stretcher bar when the screen tensioning means has been released sufhciently that the stretcher bar is clear or" the screen. Each stretcher bar is provided with a plurality of these resilient support members, which preferably are located adjacent the respective tensioning members such as bolts 33, and which bias the stretcher bar inwardly toward a position to release the screen. In the form of the invention illustrated in Fig. 2, each resilient support member is embodied by a torsion spring v38, one of which is 1 shown in greater detail in Fig. 6. As shown in this latter figure, spring 38 has a cenral portion in the form of a U-shaped loop 33a which passes downwardly and around bolt 33 and then up on the other side, the lower portion of such loop bearing against the outer face of the stretcher bar as indicated in Fig. 2. The lower portion of the loop 38a of the resilient support member engages the stretcher bar at a position below that at which the head 33b of tension bolt 33 engages the stretcher bar, thus holding the upper leg 30b of the stretcher bar in engagement with support [5 and tending to rock the stretcher bar about the position of this last-mentioned engagement. The central loop portion 38a. is disposed intermediate two spring coils 33b. At the outside end of each coil 33?) is a straight section 330 of the spring formed by a free end thereof. Each of these straight sections 380 passes downwardly through an opening t! in bar 55 fastened to, and forming a part of, support member 55. The openings 3! are sufiiciently large to receive the ends 360 of the spring easily and permit the unstressed spring to slide up and down in these openings so that it may be adjusted vertically relative to support member 15. When spring 38 is stressed or loaded by a stretcher bar, the ends of the spring are stressed and tend to assume a slightly bowed or arcuate shape which causes them to bind in openings i! in bar ii and to resist any vertical movement of the spring with respect to the support l5. It is preferable to add to stretcher bar 3d a fixed pin d2 secured thereto in such a position that it can engage the closed lower end of loop 35a of spring 38 and positively hold the stretcher bar against excessive downward movement with respect to the spring when the tensioning means 33 is released. The position of pin s2 is such as to engage the loop 33a and support the stretcher bar with the lower leg Sec thereof out of engagement with the screen when the stretcher bar is moved to released position as described hereinafter and as illustrated in Fig. 4.

When it is desired to place a tension on screen 22 or 23 in securing it in the support box if), each of the adjustable tensioning means 33 has its effective length reduced by advancing nut 35 on the bolt. As the nut is advanced, the head 33b of the bolt is drawn toward support member I5 and carries with it stretcher bar 3% The stretcher bar rocks or pivots about its engagement with support member 15, that is about the edge of the upper leg 3% of the stretcher bar which contacts the inner vertical face of said member l5. As the stretcher bar is drawn toward the support member it, the lower leg .390 of the stretcher bar moves both horizontally toward the support member and vertically downward toward the horizontal supporting surface on said support member provided by angle I5b. Thus the movement of the stretcher bar not only has a horizontal component which produces tension in the screen, but also has a vertical component which seats the edge of the screen firmly in engagement with the ledge portion of the side support member provided by angle l5b. .The spherical shape of the inner end of nut and of the seat in which it rides permits bolt '33 to move angularly with respect to the support member IE. and remain substantially perpendicular to the web 39a of stretcher bar 30.

This movement of the stretcher bar towards support member 45 brings elements 38a and 380 of torsion spring 38 closer together, and so increases the Stress in coils 38b. The natural tendency of this resilient support member 38 is to urge stretcher bar 35) in the opposite direction to the movement just described. As a result, when nut 35 is backed off to increase the effective length of the screen tensioning means, the pressure of spring 38 moves the stretcher bar and the head of bolt 33 outwardly away from the screen support member 55. This motion is'opposite to that previously described, and is basically a rocking or pivotal movement of the stretcher bar about the position of its engagement with the relatively fixed support member l5. As the lower end of the stretcher bar moves away from the side member [5, at first the tension in the screen is relaxed, and then the lower leg 360 of the stretcher bar is moved inwardly and upwardly suiiiciently that it is clear of the screen. As shown in Fig. l, the inward and upward force applied to the stretcher bar by its resilient support member 38 is sufilcient to support the stretcher bar entirely clear of the screen when the tensioning means has been released suihciently. It will be evident from a study of Fig. 4, that if it were not for the means sup-porting the stretcher bar, the bar would fall by gravity down onto the screen. As it is, the resilient support member 38 holds the stretcher bar up and away from the screen. Any tendency for the stretcher bar to slide downwardly with relation to spring 38 is limited by pin is engaging the bottom of the spring loop 38a, as shown in Fig. 4.

There is shown in Fig. 7 a modified form of my invention in which the principal difierence between it and the form previously described lies in the form of resilient member for supporting the stretcher bar clear of the screen. In this case, compression coil spring 35 surrounds bolt 33, the opposite ends of spring i5 bearing against stretcher bar 38 and the side support member l5, respectively. In order to guide spring 45, it is preferable to mount a cup at rigidly on the support member 6 5 so that the cup becomes an effective part of the screen support member. The outer end wall iber of the cup then forms a stationary base against which the outer end of spring, :25 presses, and is shown as provided with an outwardly facing spherical seat 4% engaged by the spherical inner end of nut 35.

When nut 35 is advanced on bolt 33, stretcher bar 53 is drawn toward side support member IE to the screen-securing position shown in Fig. 7 in which tension is applied to screen 23 by engagement of stretcher bar with one edge of the screen. In this position the screen is held in firm engagement with the horizontal supportm surface provided by the upper face of angle member We secured to and forming part of the side support member i5. If nut 35 is backed ofi, then stretcher bar 39 is moved inwardly and upwardly away from the support member l under the force applied by the resilient stretcher bar supporting member. This stretcher bar supporting member, spring 45, supports the stretcher bar free and clear of screen 23 in some position such as is indicated in dot-dash lines at 30 in Fig. '7 when the screen tensioning means is sufficiently released. It will be noted that spring 45 always tends to move the stretcher bar away from the screen support member in opposition to the force applied by tensioning means 33.

The motion of the stretcher bar and bolt 33 in the embodiment of Fig. '7 is largely a bodily movement in a direction axially of bolt 33. This is a somewhat different motion than is imparted to the stretcher bar by torsion spring 33 and is a result of the difference in the physical shape of, and the nature of the forces exerted by, the two types of the resilient supporting members for the stretcher bar. However, in both cases there is at least some rocking or pivotal movement of the stretcher bar about the location of its engagement with the support member 15. After the upper leg of the stretcher bar engages the frame member and the lower leg engages reinforcing strip 3| on screen 23, further tightening adjustment of the tensioning means causes the lower leg of the stretcher bar to move outwardly toward the support member I5 and slightly downwardly to seat the screen in firm engagement with the upper surface of angle member I50. Tension is applied to the screen by this pivotal movement. The amount of this movement depends upon the exact design of the several parts concerned; and for any given size of stretcher bar and screen support structure, it differs according to the width and thickness of screen 23 and the amount of stretching undergone by the screen when tension is applied to it. Of course, as nut 35 is backed off in order to release the screen tensioning means, stretcher bar 30 first rocks in the opposite direction with respect to side support member [5 about the location of engagement of these two members and is finally moved bodily away from the support member l5.

In view of the foregoing disclosure of different embodiments of my invention, it will be apparent that various changes in the construction and arrangement of parts may occur to persons skilled in the art without departing from the spirit and scope of my invention. Consequently, it is to be understood that the foregoing description is considered as illustrative of, rather than restrictive upon, the invention as defined in the appended claims.

I claim:

1. In a screening apparatus of the type in which a screen support structure carried on resilient mounting means, and a screen held in tight engagement with the support structure, are caused to vibrate together as a unit on the resilient mounting means, the combination comprising: an elongated support member forming a part of the resiliently mounted screen support structure and including an inwardly projecting ledge extending longitudinally of the support member to engage and support an edge portion of a screen; an elongated stretcher bar positioned inwardly of said support member and above said inwardly projecting ledge, movably engaging said support member and formed to engage one edge of a screen resting on said inwardly projecting ledge and tension the screen upon movement of the stretcher bar outward toward the support member; tensioning means engaging the support memher and the stretcher bar and operable to move the stretcher bar outward toward the support member and downward toward said inwardly projecting ledge to so engage and tension the screen and to hold it in tight engagement with said inwardly projecting ledge; and spring means arranged to act outward against the support memher and inward and upward against the stretcher bar in opposition to the tensioning means, to resiliently move the stretcher bar inward away from the support member and upward away from said inwardly projecting ledge when said tensioning means is released, thereby disengaging the stretcher bar from the screen resting on said inwardly projecting ledge so as to release the tension on the screen and support the stretcher bar clear of the screen and the ledge.

2. The combination as set forth in claim 1, in which the lower portion of said stretcher bar is formed and positioned to engage the edge of the screen and the upper portion of the tension member bears pivotally against the inner face of said elongated support member; and in which said spring means is interposed between said elongated support member and said stretcher bar and engages the latter intermediate said lower and upper portions thereof.

3. The combination as set forth in claim 1, in which the tensioning means comprises a bolt passing through the stretcher bar and the elongated support member with a nut thereon which when advanced moves said stretcher bar outward toward said support member and downward toward said ledge, and in which the spring means is a compression spring surrounding said bolt and bearing at its ends against said stretcher bar and said support member.

4. The combination as set forth in claim 1, in which the tensioning means comprises a bolt passing through the stretcher bar and the elongated support member with a nut thereon which when advanced moves said stretcher bar outward toward said support member and downward toward said ledge, and in which the spring means is a torsion spring having two end portions that bear outward against the elongated support member and an intermediate loop portion that passes around said bolt and bears inward and upward against the stretcher bar.

5. The combination as set forth in claim 4, in which the two end portions of the torsion spring extend vertically and slidably in openings in the elongated support member so as to be vertically adjustable when the spring is unstressed, said spring being normally held against such movement by binding action of said end portions in said openings due to stress in the spring resulting from normal loading thereof by said stretcher bar.

6. The combination as set forth in claim 4, in which the intermediate loop portion of the tension spring extends downward and engages the stretcher bar at the closed lower end of said loop portion, and said stretcher bar is provided with a pin projecting within said loop portion in position to engage the lower end thereof to limit downward movement of the stretcher bar relative to the spring.

7. The combination as in claim 1 in which the spring means is adjustably mounted on the elongated support member for up-and-down adjustin movement.

8. The combination as in claim 1 in which the spring means is a torsion spring with portions bearing against the elongated support member and portions bearing against the stretcher bar.

9. The combination as in claim 1 in which the sprin means is a coil spring with opposite ends bearing against the elongated support member 5 and the stretcher bar.

PAUL C. BYE.

REFERENCES CITED The following references are of record in the 10 file of this patent:

Number 19 UNITED STATES PATENTS Name Date Nelson Mar. 19, 1912 Pedersen Dec. 16, 1913 Ambauster Oct. 30, 1917 Fitchett July 29, 1924 Lyman et a1 May 19, 1925 Miniere -1 July 28, 1925 Warner Mar. 19, 1940 Vogel May 30, 1950 

